1. Field of the Invention
The present invention relates to a substrate processing apparatus, and more particularly, to a substrate processing apparatus for subjecting a semiconductor wafer to a process such as a film formation in a single substrate-processing manner or a small number of substrates-processing manner at a time.
2. Description of the Related Art
Conventionally, a reaction tube used with a substrate processing apparatus of a type described above has the structure shown in. FIG. 15, which is a plan view of a conventional substrate processing apparatus.
The substrate processing apparatus 200 is provided with a heater 70 and a reaction tube 80 disposed therein. The reaction tube 80 is provided with a reaction tube body 81, a reaction gas introducing tube 85 and a reaction tube flange 83. A reaction gas introducing hole 82 is provided at a central portion of an upstream of the reaction tube body 81. The reaction gas introducing tube 85 is provided in communication with an interior of the reaction tube body 81 through the reaction gas introducing hole 82. The reaction tube body 81 is provided at its downstream with the reaction tube flange 83. The reaction tube flange 83 is provided with a wafer transfer hole 84. In a state where a semiconductor wafer 90 is held in the reaction tube body 81, heating is effected by the heater 70 and a reaction gas is introduced from the reaction gas introducing hole 82 into the reaction tube body 81, and is exhausted from the wafer transfer hole 84 of the reaction tube flange 83, thereby processing the semiconductor wafer 90 such as to achieve film formation.
According to the conventional reaction tube 80, however, the reaction gas is introduced into the reaction tube 80 without being sufficiently heated and therefore, a temperature of the reaction gas upstream of the semiconductor wafer 90 is lowered, and there is a problem that a thickness of a film formed on the semiconductor wafer 90 becomes nonuniform.